In a Wideband Code Division Multiple Access system, a Radio Access Network (RAN) normally comprises one Radio Network Controller (RNC) and one base station, such as a Radio Base Station, where the latter is responsible for transmitting data over the air interface. For best effort Quality of Service two different transport network congestion control algorithms are used to provide that user data is available in the base station for scheduling.
In a traditional algorithm the RNC shapes the traffic down to the base station in order to maintain the amount of user data in a user data buffer constant in time in the base station.
In a more recent algorithm the RNC does not shape the user data traffic and instead the RBS is in theory the only RAN node with a buffer for buffering of user data. The user data traffic volume in a base station buffer, as well as in buffer(s) in the Transport Network (TN) is typically controlled by introducing a packet discard functionality on user data. This is demonstrated in patent application WO2011120581A1.
The packet discard functionality being used therein operates on a per Radio Access Bearer (RAB) level. This means that the bit rate is measured per RAB and that any packet in the RAB is discarded when resolving a detected congestion.
Applying this packet discard functionality to the Transmission Control Protocol (TCP) operating per TCP flow, packet would be discarded per TCP flow. A packet would thus be discarded from the TCP flow in which congestion was detected.
The TCP response to a packet discard depends on characteristics of the TCP flow, such as TCP flow bit rate or recent discards on the same TCP flow.
Said packet discard functionality works conceptually well in a single service scenario with a single TCP flow, due to that an introduced packet discard always occurs on the only existing TCP flow and therefore reduces the rate of this flow, i.e. the requested behavior is achieved. In other words, there is a one-to-one mapping between RAB and the TCP flow.
In today's smartphone- and Personal Computer dongle-dense networks, a large extent of the users have multiple ongoing services as well as services with multiple TCP flows involving web browsers, Peer-to-Peer (P2P) traffic etc. This creates a scenario with multiple flows, within one Radio Access Bearer (RAB). Within such a scenario an Internet Protocol (IP) packet discard functionality according to the packet discard functionality, as mentioned above, may select and hit a packet belonging to any of the ongoing TCP flows within the RAB that experiences a detected congestion. However, if the flow within which the RAB is hit is an incorrect flow, i.e. for instance a flow that does not react to packet discards, that is associated with a high priority application or has a very low bit-rate, the effect will be that no or a very limited rate reduction within the RAB is achieved. This erroneous attempt to regulate the bit-rate will in turn result in a higher packet loss rate in the TN. The increased packet loss rate causes a reduced end user performance both at congestion in the TN and/or at the Uu interface, i.e. the air interface between the base station and a User Equipment served by said base station.
There is hence a need for an improvement of the congestion control in a communication network.